The heart of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of the rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head includes a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a gap layer at an air bearing surface (ABS) of the write head and the pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic flux in the pole pieces which causes a magnetic field to fringe out at a write gap at the ABS for the purpose of writing the aforementioned magnetic impressions in tracks on the moving media, such as in circular tracks on the aforementioned rotating disk.
In recent read head designs a spin valve sensor, also referred to as a giant magnetoresistive (GMR) sensor, has been employed for sensing magnetic fields from the rotating magnetic disk. The sensor includes a nonmagnetic conductive layer, hereinafter referred to as a spacer layer, sandwiched between first and second ferromagnetic layers, hereinafter referred to as a pinned layer and a free layer. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. The magnetization of the pinned layer is pinned perpendicular to the air bearing surface (ABS) and the magnetic moment of the free layer is located parallel to the ABS, but free to rotate in response to external magnetic fields. The magnetization of the pinned layer is typically pinned by exchange coupling with an antiferromagnetic layer.
The thickness of the spacer layer is chosen to be less than the mean free path of conduction electrons through the sensor. With this arrangement, a portion of the conduction electrons is scattered by the interfaces of the spacer layer with each of the pinned and free layers. When the magnetizations of the pinned and free layers are parallel with respect to one another, scattering is minimal and when the magnetizations of the pinned and free layer are antiparallel, scattering is maximized. Changes in scattering alter the resistance of the spin valve sensor in proportion to cos θ, where θ is the angle between the magnetizations of the pinned and free layers. In a read mode the resistance of the spin valve sensor changes proportionally to the magnitudes of the magnetic fields from the rotating disk. When a sense current is conducted through the spin valve sensor, resistance changes cause potential changes that are detected and processed as playback signals.
In the face of the ever increasing demand for improved data rate and data capacity, researchers continually strive to decrease the size and increase the write performance of write elements. One recently constructed write head, termed a bionic head, has been manufactured by Hitachi Global Storage Technologies. The bionic head includes a first pole (P1) that includes a first layer of magnetic material, and a magnetic pedestal (P1 pedestal) formed on that first layer of magnetic material. A thin layer of dielectric material is formed over the top of the P1 pedestal, and the second pole extends over the first pole from the pole tip region to the back gap. The bionic head provides excellent track width control, bit size and magnetic field strength.
Write heads, such as the bionic head described above, have suffered from recession. Recession of the P1 pedestal is a term that refers to the P1 pedestal sinking into the write head (ie. away from the magnetic medium). As can be appreciated, this recession of the pedestal portion of the first pole increases the effective fly height of the write head. As slider fly heights decrease, the effect of this recession becomes a larger percentage of the fly height budget, seriously degrading write performance. To maintain performance standards, manufacturers must specify a maximum allowable level of recession. A head having recession greater than this amount must be scrapped. Currently yield losses due to recession have been as high as 0.5%.
Therefore, there is a strong felt need for a way of reducing recession in the construction of a write head such as a bionic head. Such a means for reducing recession would preferably involve existing manufacturing techniques and materials so as not require significant additional manufacturing expense. Such a method would also preferably not negatively affect other performance parameters such as track width control, write gap thickness, or field strength among others.